1. Field of the Invention
The present invention relates to method and apparatus for coating material such as the resist onto a matter to be processed.
2. Description of the Related Art
The spin coating method is often employed for the resist-coating process in the course of manufacturing semiconductor devices. According to the spin coating method, a spin chuck 2 is rotatably housed in a spin cup 1 which is opened outside at the top thereof, as shown in FIG. 3. A matter or wafer 3 to be processed is sucked and fixed on the spin chuck 2. Resist 5 is dropped onto the wafer 3 through a nozzle 4 while rotating the spin chuck 2. The resist 5 on the wafer 3 is spread uniformly by centrifugal force to form a resist film 6 on the wafer 3.
Solvent is mixed in the resist 5 in this case to keep the resist viscous and the resist film 6 on the wafer 3 is hardened while causing the solvent to be volatilized.
The wafer 3 on which the resist film 6 has been formed is then carried to the next baking process.
According to this coating method, however, rotation speed at the center area of the wafer 3 is different from that at the circumferential area thereof. Therefore, the evaporation rate of the solvent in the resist 5 is different at the center and circumferential areas of the wafer 3. When the resist 5 dropped on the wafer 3 in the center thereof is spread toward the circumference thereof, the amount of the solvent contained in the resist 5 is changed by increasing evaporation rate of the solvent along the radius of the wafer 3 due to the increase of the rotation speed, thereby change the viscosity of the resist 5 in the correspondence with the distance from the center of the wafer 3. As shown in FIG. 4, therefore, the resist film 6 is hardened while leaving it thicker at the circumferential area of the wafer 3. As the result, the resist film 6 does not become uniform all over the wafer 3, thereby causing the productivity of semiconductor devices to be lowered.